restore full equation

do not solve the equation, even though some members cancel each other,
this is done for clarity,
we'll let the compiler do the resolution at compile time.

lib/compress/zstd_compress.c

@@ -7342,7 +7342,7 @@ size_t ZSTD_convertBlockSequences(ZSTD_CCtx* cctx,
                 DEBUGLOG(5, "long literals length detected at pos %zu", longl-nbSequences);
                 assert(longl <= 2* (nbSequences-1));
                 cctx->seqStore.longLengthType = ZSTD_llt_literalLength;
-                cctx->seqStore.longLengthPos = (U32)(longl-nbSequences);
+                cctx->seqStore.longLengthPos = (U32)(longl-(nbSequences-1)-1);
             }
         }
     } else {